You get whacked in the head enough times, you flinch when somebody makes the slightest move.

That’s what has happened with the Democrats and the federal transportation spending plan, which expires Sept. 30. House Republicans have made only faint gestures toward rejecting an extension and Democrats are getting jumpy. But who can blame them?

It’s a fight Democrats shouldn’t have to wage (and might avoid), but they’re taking no chances. They’ve launched pre-emptive strikes to warn House Republicans to stay away from the political hostage-taking that drove the country to the brink of default in a battle over the debt ceiling.

President Obama has cautioned Republicans to keep their hands off transportation funding, which has been extended seven times previously. Congressional Democrats and lobbyists have issued warnings, too. If the bill expires, Obama said, “over 4,000 workers will be furloughed immediately.” With an 18.4-cent-per-gallon federal gas tax included in the plan, transportation funds would dry up.

Rep. John L. Mica (R-Fla.), chairman of the House Transportation Committee and the villain in the FAA shutdown, says this is the last highway program extension to which he will agree.

The FAA extension expires Sept. 16 and the transportation funding would run out two weeks after that. There should be clean extensions of both, but Republicans might add strings to one or both.

Renewing the gas tax may be seen by tea party members as a tax increase. Some might want cuts in domestic spending; others might target Amtrak. Says Sen. Barbara Boxer (D-Calif.): “I don’t count on anything going smoothly anymore.”

If any spending could move into the left lane, this should be it. The federal government spends approximately $42 billion a year on transportation projects, and without an extension, government workers will lose their pay and jobs will be lost among contractors, manufacturers and suppliers.

This type of game-playing could shove the nation into a double-dip recession.

In a different political climate, Congress could pass a sensible, long-term transportation plan. But for now, we can only root for the status quo. America’s infrastructure needs the money now.